Describe OpenCL C changes

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194368 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ReleaseNotes.rst

@@ -112,6 +112,13 @@ Objective-C Language Changes in Clang
 
 ...
 
+OpenCL C Language Changes in Clang
+----------------------------------
+
+- OpenCL C "long" now always has a size of 64 bit, and all OpenCL C
+  types are aligned as specified in the OpenCL C standard. Also,
+  "char" is now always signed.
+
 Internal API Changes
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